Sheets of apertured films, woven fabrics and nonwoven materials are widely used in many types of products such as, for example, personal care products, garments, medical fabrics and the like. Some sheets made from certain inexpensive raw materials could have an even wider range of applications in these products if the sheets could be designed to have enhanced properties or attributes.
For example, polyolefins are widely used in the manufacture of sheets of apertured films, woven fabrics, and nonwoven materials. Many types of polyolefin sheets tend to be hydrophobic and relatively inert. That is, the low surface free energy of polyolefins (e.g., polypropylene) and their relatively chemically inert nature render many unmodified polyolefins ill-suited for providing attributes other than those based on hydrophobic interactions.
In the past, chemical coatings and/or internal additives have been added to sheets of materials to impart desired properties. Many of these coatings and/or additives present problems related to cost, effectiveness, durability and/or the environment.
It has been proposed that biofunctional materials (e.g., proteins) can be deposited from solutions onto different substrates (i.e., sheets of materials) to modify the surface properties of the substrates and/or serve as a functionalized surface that can be chemically reactive. However, many of the economically desirable substrates (e.g., substrates formed of polymers such as polyolefins) have surfaces that are unsuitable for the rapid and inexpensive deposition of biofunctional materials, especially when durable, tightly-bound coatings of satisfactory adherence are desired.
It has also been proposed that surfaces of these substrates can be modified to improve the adherence of biofunctional materials. Some suggested surface modification techniques involve: 1) irradiating the surface of a polymeric material in the presence of oxygen to create active sites and then chemically grafting a polymer onto the active sites; 2) providing an organic surface coating by plasma discharge in the presence of a plasma polymerizable, halogenated hydrocarbon gas; and 3) treating (e.g., oxidizing) the surface of a substrate so that it has a hydrophilic character with a high amount of cation-exchange groups.
Such treatments can be complex, expensive, environmentally unsuitable, leave trace amounts of undesirable compounds, unsuited for high-speed manufacturing processes, and/or cause degradation of the substrate. In particular, a trend toward increasing environmental awareness and government regulation in the areas of air, water, product and food quality make some of these treatments relatively unattractive. Furthermore, these treatments fail to address the need for a practical method of depositing a durable, tenacious coating of proteins on the unmodified surface (or surfaces) of a relatively inert, hydrophobic substrate.
Thus, there is still a need for a simple method of producing a durable and chemically reactive protein coating on an unmodified, relatively inert, hydrophobic substrate. A need exists for a practical method of producing a durable and chemically reactive protein coating on an unmodified, relatively inert, polyolefin substrate. A need exists for a pattern or gradient of surface modification on a relatively inert, hydrophobic substrate. There is also a need for a protein-coated fibrous and/or apertured film-like material having a protein coating such that the resulting coated material can generally be considered wettable. A need also exists for fibrous and/or apertured film-like substrates formed from a relatively inert, hydrophobic material (e.g., a polyolefin) that are coated with a readily available, inexpensive, natural, renewable and nontoxic material, especially if such a coated material can be produced in a high-speed manufacturing process. Meeting these needs are important since it is both economically and environmentally desirable to substitute relatively complex chemical surface modification and/or functionalization of inexpensive (and often recyclable) substrates with inexpensive, readily available natural materials.